Int. J. Environ. Res. Public Health 2013, 10, 3886-3907; doi:10.3390/ijerph10093886

International Journal of

Environmental Research and

Public Health ISSN 1660-4601

www.mdpi.com/journal/ijerph

Review

Pulmonary Oxidative Stress, Inflammation and Cancer:

Respirable Particulate Matter, Fibrous Dusts and Ozone as

Major Causes of Lung Carcinogenesis through Reactive Oxygen

Species Mechanisms

Athanasios Valavanidis *, Thomais Vlachogianni, Konstantinos Fiotakis and Spyridon Loridas

Department of Chemistry, University of Athens, University Campus Zografou, Athens 15784, Greece;

E-Mails: thvlach@chem.uoa.gr (T.V.); cfiot@chem.uoa.gr (K.F.); spiroslor@chem.uoa.gr (S.L.)

* Author to whom correspondence should be addressed; E-Mail: valavanidis@chem.uoa.gr;

Tel.: +30-210-727-4763; Fax: +30-210-727-4761.

Received: 15 May 2013; in revised form: 24 July 2013 / Accepted: 15 August 2013 /

Published: 27 August 2013

Abstract: Reactive oxygen or nitrogen species (ROS, RNS) and oxidative stress in the

respiratory system increase the production of mediators of pulmonary inflammation and

initiate or promote mechanisms of carcinogenesis. The lungs are exposed daily to oxidants

generated either endogenously or exogenously (air pollutants, cigarette smoke, etc.). Cells

in aerobic organisms are protected against oxidative damage by enzymatic and non-enzymatic

antioxidant systems. Recent epidemiologic investigations have shown associations between

increased incidence of respiratory diseases and lung cancer from exposure to low levels of

various forms of respirable fibers and particulate matter (PM), at occupational or urban air

polluting environments. Lung cancer increases substantially for tobacco smokers due to the

synergistic effects in the generation of ROS, leading to oxidative stress and inflammation

with high DNA damage potential. Physical and chemical characteristics of particles (size,

transition metal content, speciation, stable free radicals, etc.) play an important role in

oxidative stress. In turn, oxidative stress initiates the synthesis of mediators of pulmonary

inflammation in lung epithelial cells and initiation of carcinogenic mechanisms. Inhalable

quartz, metal powders, mineral asbestos fibers, ozone, soot from gasoline and diesel

engines, tobacco smoke and PM from ambient air pollution (PM10 and PM2.5) are involved

in various oxidative stress mechanisms. Pulmonary cancer initiation and promotion has

been linked to a series of biochemical pathways of oxidative stress, DNA oxidative

damage, macrophage stimulation, telomere shortening, modulation of gene expression and

OPEN ACCESS

Int. J. Environ. Res. Public Health 2013, 10 3887

activation of transcription factors with important role in carcinogenesis. In this review we

are presenting the role of ROS and oxidative stress in the production of mediators of

pulmonary inflammation and mechanisms of carcinogenesis.

Keywords: reactive oxygen species; oxidative stress; inflammation; mechanisms of

carcinogenesis; respirable particulate matter; ozone; tobacco smoke

1. Introduction

Studies of pulmonary carcinogenicity and respiratory inflammation have shown high risk for

respiratory diseases and lung carcinogenesis in humans from exposures to various inhalable dusts,

mineral fibers, airborne particulate matter (PM) and ozone. Ambient air pollution, containing PM

smaller than aerodynamic diameter of 2.5 μm (PM2.5), has gained particular attention in recent years as

a causative factor in the increased incidence of respiratory diseases, including lung cancer [1–4].

Tobacco smoke also plays a very important role in increasing the risk for epithelial inflammation and

lung cancer due to its high carcinogenic potential and the synergistic effects with other respirable

particulate to generate reactive oxygen species (ROS) and catalyze redox reactions in human lung

epithelial cells, leading to oxidative stress and increased production of mediators of pulmonary

inflammation [5–9].

Airborne PM is an important pollutant of urban atmosphere and has been linked to adverse health

effects of the respiratory system. Particles can penetrate into the respiratory airways and deposited in

the respiratory bronchioles and the alveoli. PM from combustion sources contain a number of

constituents that generate ROS by a variety of reactions. The most important are transition metals with

redox properties, persistent free radicals, redox-cycling of quinones, polycyclic aromatic hydrocarbons

(PAHs) and volatile organic compounds (VOCs) which may be metabolically activated to ROS that

can react to form bulky adducts or strand breaks on cellular DNA [10,11].

In recent years a number of publications have linked air pollution particle exposure to oxidation of

DNA in cells, tissues, or their metabolites in urine of rodents and humans. Studies have investigated

the effect of diesel exhaust particles (DEP) or ambient air pollutants in terms of oxidized DNA

nucleobases. In nuclear and mitochondrial DNA (mtDNA) a free radical-induced oxidative lesion has

been used widely as a predominant biomarker for oxidative stress. 8-Oxo-7,8-dihydroguanine

(8-oxoGua) can be measured quantitatively by HPLC and GC-MS in animal and in human

biomonitoring studies [12–15].

Additionally, other air pollutants contribute to oxidative stress in the pulmonary system and play a

role in synergistic redox effects. Ozone as a pulmonary irritant causes oxidative stress, inflammation

and tissue injury. Also, evidence suggests that macrophages play a role in the pathogenic pulmonary

responses. Studies showed that bronchiolar epithelium is highly susceptible to injury and oxidative

stress induced by acute exposure to ozone, accompanied by altered lung functioning [16]. Another

study showed that exposure of rats to ozone resulted in increased expression of 8-hydroxy-2′-

deoxyguanosine (8-OHdG), as well as heme oxygenase-1 (HO-1) in alveolar macrophages [17].

Epidemiological and clinical studies showed that people exposed to combined air pollutants, such as

Int. J. Environ. Res. Public Health 2013, 10 3888

ozone and cigarette smoke or PM showed increased pulmonary oxidative stress and inflammation

associated with an increase in pulmonary diseases and mortality [18].

2. Why Aerobic Organisms are Susceptible to Oxidative Stress, Inflammation and Degenerative

Diseases?

All aerobic biological systems use oxygen as an essential part of their physiological cellular

metabolic processes. At moderate concentrations oxygen free radicals, or more generally, reactive

oxygen species (ROS) and reactive nitrogen species (RNS), are products of normal cellular

metabolism. Aerobic organisms generates energy in the mitochondria of eukaryotic cells and most of

these ROS and RNS physiological and beneficial; however, less than 5% of them can be toxic for the

cell if their concentration increases. These normally low-concentration compounds that are derived

from oxidative metabolism are necessary for certain subcellular events, including signal transduction,

enzyme activation, gene expression, etc. [19,20].

ROS are produced in cellular sites by electron transfer reactions through enzymatic and

non-enzymatic processes. The main sources of ROS in all cells of aerobic organisms are mitochondria,

cytochrome P450 and peroxisomes. Under physiological conditions, there is a constant endogenous

production of reactive intermediates of radical species of oxygen and nitrogen that interact as

regulatory mediators of signaling processes for metabolism, cell cycle, intercellular transduction

pathways, cellular redox systems and mechanisms of apoptosis [19–23]. At higher concentrations,

free radicals and ROS are hazardous for living organisms and can cause oxidative damage to all major

cellular constituents (membrane lipids, proteins, enzymes, DNA). Many of the ROS-mediated responses

actually protect the cells against oxidative stress and re-establish ―redox homeostasis‖. Excessive or

sustained increase in ROS production, which if not balanced by antioxidant enzymes and non-enzymatic

cellular antioxidant defences, has been implicated in chronic inflammatory conditions, malignant

neoplasms, diabetes mellitus, atherosclerosis and various neurodegenerative diseases [24–28].

Reactive organic species in aerobic organisms can be classified into four groups: ROS, reactive

nitrogen species (RNS), reactive sulfur species (RSS) and reactive chlorine species (RCS). ROS are

the most abundantly produced and have highly oxidative properties which can damage essential

cellular components. If ROS and the other reactive species are not balanced by antioxidant enzymes

and non enzymatic antioxidant substances with low molecular mass. The most important ROS include

superoxide anion (O2−·), hydrogen peroxide (H2O2), the most reactive hydroxyl radical (HO·), singlet

oxygen (1O2), ozone (O3) and others. The most abundant RNS is nitric oxide (NO·), which is able to

react with certain ROS, including the peroxynitrite anion (ONOO−, interaction of O2

−· and NO·).

Nitric oxide can be converted into peroxynitrous acid and ultimately into hydroxyl radical and nitrite

anion (NO2−) [29]. All aerobic organisms evolved antioxidant defences to protect themselves against

ROS generated in vivo. These antioxidants can intercept, scavenge, neutralize radicals and reactive

intermediates generated in excess under physiological conditions. The most important antioxidant

enzymes are the superoxide dismutase (SOD), the catalase (CAT), the glutathione redox system

(glutathione peroxidase and glurtathione-S-transferase) [30,31]. Also, low molecular mass antioxidant

compounds are ascorbic acid (vitamin C), vitamin E (tocopherol), uric acid, bilirubin, glucose,

caeruloplasmin, etc., and proteins that bind metal ions in forms unable to accelerate free radical

Int. J. Environ. Res. Public Health 2013, 10 3889

reactions. These defences are very useful in the protection of aerobic organisms from oxidative

damage, such as lipid peroxidation, protein or enzyme oxidation and DNA oxidative damage

(mutations) [32].

Oxidative stress results when ROS or RNS are not adequately removed or neutralized, because of

depleted antioxidant defences of increases beyond their capacity. The balance between oxidants and

antioxidants ―redox homeostasis‖, is a crucial event in living organisms. Subjecting cells to oxidative

stress can result in severe metabolic dysfunction and other oxidative damages to proteins,

carbohydrates, DNA, RNA, mtDNA and membrane lipids [33–35].

Carcinogenesis is a multistep process in three stages: initiation, promotion and progression leading

to malignant tumours [36,37]. During these stages various genetic and epigenetic events occur that

lead to the progressive conversion of normal cells into cancer cells. In cellular prooxidant states ROS

are overproduced, thus initiating oxidative damage to cellular DNA (cDNA) and mitochondrial DNA.

The biological consequences are mutations, chromosomal aberrations, sister chromatid exchanges,

etc., that lead to cellular degeneration, carcinogenesis and ageing. ROS play a role mostly in the

promotion stage of carcinogenesis, during which gene expression of initiated cells is modulated by

affecting genes that regulate cell differentiation and growth. In the progression stage, benign

neoplasms are stimulated to more rapid growth and malignancy [38,39].

3. Oxidative Stress, Inflammation and Carcinogenesis

Oxidative damage is considered to play a pivotal role in ageing, several degenerative diseases and

cancer. Acute and chronic inflammation has been correlated with increased risk for various malignant

neoplasms from a great number of clinical and other studies. The possible mechanisms by which

inflammation can contribute to carcinogenesis include genomic instability, alterations in epigenetic

events and subsequent inappropriate gene expression, enhanced proliferation of initiated cells,

resistance to apoptosis, aggressive tumour neovascularization, invasion through tumour-associated

basement membrane, angiogenesis and metastasis [40–42]. Inflammatory cells are particularly

effective in generating most of the reactive oxygen species. The activation of the redox metabolism of

the inflammatory cells generates a highly oxidative environment within an organ of aerobic organisms.

Much of the oxygen biochemistry, through the activation of plasma membrane NADPH oxidase, of

macrophages and neutrophils is directed towards the release of superoxide anion, hydrogen peroxide

and hydroxyl radicals [43–48].

Inflammation acts through the formation of ROS and RNS which cause oxidative damage to

cellular components. Many proinflammatory mediators, especially cytokines, chemokines and

prostagladins, turn on the angiogenesis switches mainly controlled by vascular endothelial growth

factors [49,50].

Cancer-associated inflammation is also linked with immune-suppression that allows cancer cells to

evade detection by the immune system. Inflammation is a critical component of tumour progression.

Many cancers arise from sites of infection, chronic irritation and inflammation. It is now becoming

clear that the tumour microenvironment, which is largely orchestrated by inflammatory cells, is an

indispensable participant in the neoplastic process, fostering proliferation, survival and migration.

In addition, tumour cells have co-opted some of the signalling molecules of the innate immune system,

Int. J. Environ. Res. Public Health 2013, 10 3890

such as selectins, chemokines and their receptors for invasion, migration and metastasis. These insights

are fostering new anti-inflammatory therapeutic approaches to cancer development [51]. Pathological

angiogenesis is a hallmark of cancer and various ischaemic and inflammatory diseases. Chronic

inflammation is associated with angiogenesis, a process that helps cancer cells to grow. Angiogenesis

is necessary for expansion of tumor mass. Macrophage, platelets, fibroblasts and tumour cells are a

major source of angiogenic factors (vascular endothelia growth factors, chemokines, NO, etc.) [52–54].

The inflammation in the tumour microenvironment is characterized by leukocyte infiltration,

ranging in size, distribution and composition, as: tumor-associated macrophages (TAM), mast cells,

dendritic cells, natural killer (NK) cells, neutrophils, eosinophils and lymphocytes. These cells produce

a variety of cytotoxic mediators such as ROS and RNS, serine and cysteine proteases, membrane

perforating agents, matrix metalloproteinase (MMP), tumour necrosis factor α (TNFα), interleukins

(IL-1, IL-6, IL-8), interferons (IFNs) and enzymes, as cyclooxygenase-2 (COX-2), lipooxygenase-5

(LOX-5) and phospholipase A2 (PLA2). Other researchers discovered that tumour-associated

macrophages are key regulators of the link between inflammation and carcinogenesis [55,56].

4. Particulate Matter, ROS, Oxidative Stress and Inflammation

The main current paradigm in respirable particular matter toxicology is centred on the

concept of oxidative stress. The ability of respirable particles or fibrous dusts to penetrate the

respiratory system and reach the lung alveoli in order to generate ROS and other oxidants or free

radicals is suggested to be the main factor involved in their pathogenic potential. There is abundance

of scientific evidence for ROS involvement in lipid peroxidation, DNA mutations and protein

(enzyme) oxidative damage [57–59].

The term ―oxidative stress‖ is defined as the adverse condition resulting from an imbalance in

cellular oxidants (mostly ROS and nitrogen free radicals) and antioxidants (enzymatic, such as CAT

and SOD, and small molecular compounds with antioxidant properties, such as ascorbic acid). But

small amounts of ROS and RNS are similarly very important for various biochemical processes and

intracellular signaling [60]. Redox homeostasis is very important for aerobic organisms. It is governed

by the presence of large pools of these antioxidants that absorb and buffer reductants and oxidants.

Most importantly, antioxidants provide essential information on cellular redox state, and they influence

gene expression associated with biotic and abiotic stress responses to maximize defense. Growing

evidence suggests a model for redox homeostasis in which the ROS–antioxidant interaction acts as a

metabolic interface for signals derived from metabolism and from the environment. This interface

modulates the appropriate induction of acclimation processes or, alternatively, execution of cell death

programs [61]. Oxidative stress is the responsible factor for the rise of pulmonary pathology through

airway inflammation, particularly when humans are exposed to inhalable airborne PM [62,63].

Experimental studies showed that airborne PM, like tobacco smoke, produce ROS that have been

implicated in the activation of mitogen-activated protein kinase (MAPK) family members and

activation of transcription factors such as NF-κB and AP-1 (the activator protein 1). These signaling

pathways have been implicated in processes of inflammation, apoptosis, proliferation, transformation

and differentiation [64]. Airborne PM represents a mixture of many different components that consists

of a variable particle core and a large array of surface-bound constituents including PAHs and heavy

Int. J. Environ. Res. Public Health 2013, 10 3891

metals. Also, studies showed that stable free radicals in the PM, as well as in cigarette tar play an

important role in increasing ROS production, especially hydroxyl radicals [65–67].

The most important ROS is considered the hydroxyl radicals (HO·) via Fenton reaction where

metals can be oxidized by hydrogen peroxide (Fe2+

+ H2O2 → Fe3+

+ HO− + HO·). It is very reactive

and is widely considered to be responsible for damage to DNA and lipid peroxidations [68,69]. Studies

showed that airborne particulates have absorbed numerous reactive organic compounds on their porous

surface which can release ROS via quinone redox cycling [70]. PAHs can be converted to quinones

within the lung tissues by biotransformation enzymes such as cytochrome P450, epoxide hydrolase

and dihydrodiol dehydrogenase [71,72].

Synergistic mechanisms of inhalable particulate matter (penetrating deep into the lung’s alveoli)

and other components of air pollution (ozone, nitric oxide, soot, heavy metals, PAHs) and tobacco

smoke have been studied. The porous surfaces of airborne particles provide a fertile ground for

catalyzing the increased generation of ROS or other damaging oxidants which are potential initiators

of pulmonary carcinogenesis. Synergistic effects for increased ROS formation have been

experimentally verified [72].

Synergistic effects for increasing ROS generation has been verified by various experimental

studies. Increasing ROS generation has been observed: between ambient transition metals and PM

quinoids [73], for air pollution PAHs and tobacco smoke [74], for cigarette tar and nitric oxide [75],

between soot (impure carbon particles from the incomplete combustion) and iron particles [76],

between components of air pollution with aerodynamic diameter PM10 [77], between airborne PM and

ozone [78,79], between tobacco smoke and PM stable free radicals [80], between mineral fibes and

tobacco smoke [81] and between ambient air MP and wood smoke PM [82].

Aside from direct generation by the airborne particles and other inhalable materials, ROS can be

generated by target cells such as lung epithelial cells and pulmonary macrophages upon interaction

with and/or uptake of particulate material. Phagocytic cells of the innate immune system such as

alveolar macrophages (AM) and polymorphonuclear neutrophils (PMN) are highly proficient

producers of ROS to enhance microbicidal conditions in phagocytic vacuoles and eliminate pathogenic

bacteria or potentially harmful particles [83,84]. Resident macrophages in the airways and the alveolar

spaces can release ROS/RNS after phagocytosis of inhaled particles. These macrophages also release

large amounts of TNF-alpha), a cytokine that can generate responses within the airway epithelium

dependent upon intracellular generation of ROS/RNS. As a result, signal transduction pathways are set

in motion that may contribute to inflammation and other pathobiological damage in the lung airways.

Such effects include increased expression of intercellular adhesion molecule 1, interleukin-6, cytosolic

and inducible nitric oxide synthase, manganese superoxide dismutase (MnSOD), cytosolic

phospholipase A2, and hypersecretion of mucus. Ultimately, ROS/RNS may play a role in the global

response of the airway epithelium to particulate pollutants via activation of kinases and transcription

factors common to many response genes. Thus, defense mechanisms involved in responding to

offending particulates may result in a complex cascade of events that can contribute to airway

pathology [85].

Phagocyte-generated reactive species include superoxide anion (O2−·), nitric oxide, free radical

(NO·), hydrogen peroxide (H2O2), the extremely reactive hydroxyl radical (HO·), the highly oxidant

peroxynitrite (ONOO−) and hypochlorous acid (HOCl) [86]. Additionally, myeloperoxidase (MPO)

Int. J. Environ. Res. Public Health 2013, 10 3892

can produce the highly toxic product HOCl from H2O2 and chloride anions. Another phagocyte

anti-microbial system is the enzyme inducible nitric oxide synthase (iNOS), which generates NO·

radicals from L-Arginine, NADPH and oxygen. The principal cellular source of NO· in the lung are the

macrophages, with neutrophils representing another source. Also, as iNOS is expressed in airway

epithelium, lung epithelial cells release NO· in response to inflammatory stimuli such as endotoxin and

cytokines. Superoxide anion formed by NADPH oxidase (NOX) can react with NO· formed by iNOS

to produce the highly oxidant peroxynitrite ONOO− [87].

Although ROS and RNS production is a crucial event in host defence, they are capable of causing

damage to cellular macromolecules such as nucleic acids, lipids and proteins. In a chronic

inflammatory setting, persistent production of ROS can cause considerable tissue damage. Therefore,

people suffering from chronic inflammatory diseases, especially those localised to or affecting the

pulmonary region, may be susceptible for adverse health effects of PM inhalation [88]. It is well

known that ROS/RNS are capable of causing DNA strand breaks and DNA oxidation, factors that are

implicated in the initiation stage of carcinogenesis. One of the major products of oxidative DNA

damage is the premutagenic lesion 8-hydroxy-2′-deoxyguanosine (8-OHdG). Several in vitro studies

have demonstrated that PM induces DNA damage in the form of strand breaks and 8-OHdG formation

in lung epithelial cells [89,90]. Ambient particulate matter has been the focus of numerous

toxicological studies and the generation of ROS in pulmonary cells is considered the most important

mechanism for carcinogenesis [91].

5. Endogenous and Exogenous ROS, Lipid Peroxidation and DNA Damage

Endogenous and exogenous oxidative damage to DNA of aerobic cells from attack by ROS is very

frequent and is accepted after numerous measurements as an experimental fact. It has been estimated

that one human cell is exposed daily to approximate 103–10

5 hits by HO· alone. The highly reactive

HO· reacts with the heterocyclic DNA nucleobases and the sugar moiety near or at diffusion-controlled

rates leading to adduct radicals [92–95].

The mitochondrial DNA is very gene dense and encodes factors critical for oxidative

phosphorylation but it is exposed to greater oxidative damage due to the mistakes that occur during the

production of ATP through the electron transport chain Mutations of mtDNA cause a variety of human

mitochondrial diseases and are also heavily implicated in age-associated diseases, such as cancer, and

aging. There has been considerable progress in understanding the role of mtDNA mutations in human

pathology during the last two decades, but important mechanisms in mitochondrial genetics remain to

be explained at the molecular level. In addition, mounting evidence suggests that most mtDNA

mutations may be generated by replication errors and not by accumulated damage [96].

Analytical measurements of the oxidative DNA damage, as the adduct 8-oxo-2′-deoxyguanosine

(8-oxodG) in mitochondrial DNA (mtDNA), proved that it suffers greater endogenous oxidative

damage than nuclear DNA (cDNA) because of its proximity to the mitochondrial electron transport

chain, lack of protective histones and less efficient repair mechanisms [97–99]. DNA damage and

increasing numbers of mutations driving the malignant transformation process. Recent evidence also

indicates that the resulting mutated cancer-causing proteins feedback to amplify the process by directly

affecting mitochondrial function in combinatorial ways that intersect to play a major role in promoting

Int. J. Environ. Res. Public Health 2013, 10 3893

a vicious spiral of malignant cell transformation. Consequently, many malignant processes involve

periods of increased mitochondrial ROS production when a few cells survive the more common

process of oxidative damage induced cell senescence and finally death [100].

Airborne PM generated from combustion of fuels have a high potential for the formation of ROS

that deplete endogenous antioxidants, alter mitochondrial function and produce oxidative damage to

lipids, enzymes and DNA. Surface area, redox reactivity and chemical composition play important

roles in the oxidative potential of particulates. Biomonitoring studies in humans have shown

associations between exposure to air pollution and wood smoke particulates and high rates of oxidative

damage to DNA [101]. According to experimental studies on the elucidation of mechanisms by

oxidative DNA damage contributes to the development of carcinogenesis, there are at least two

different mechanisms thought to play an important role. The first mechanism is thought to act through

the modulation of gene expression affecting intracellular signaling pathways, whereas the second is

thought to proceed through the induction of genetic damage (mutations, strand breaks, chromosomal

rearrangements) and a blockage to the DNA replication [102,103].

Studies showed that modulation of gene expression by ROS and RNS and the resulting oxidative

stress is an important mechanism of carcinogenesis. Epigenetic effects on gene expression can lead to

the simulation of growth signals and proliferation. Oxidative stress causes strand breakage of DNA

and incomplete enzymatic repair mechanisms that lead to chromosomal changes. These changes in

turn contribute to genetic amplification, alterations in gene expression and loss of heterozygosity,

resulting in the promotion of mechanisms of progression of carcinogenesis [104–106].

Direct evidence of the generation of ROS, activation of redox sensitive transcription factors

(NF-kappaB, AP-1 and Nrf2) and alteration of ROS-related gene expression have been proved

experimentally with various carcinogenic metals [Cd, As, Ni, Cr(VI)]. Transition metals have been

measured in substantial concentrations in urban air pollution PM. In addition to oxidative DNA

damage, metals cause changes in DNA methylation and histone modifications, leading to epigenetic

silencing or reactivation of gene expression [107–109]. In vivo experiments showed that in

iron-induced carcinogenesis there are target genes and oxidative DNA damage [110]. In the second

mechanism ROS and RNS cause genetic mutations and chromosomal rearrangements [111].

One of the most important and widely studied oxidative DNA damage is the adduct of hydroxyl

radicals on DNA nucleobases, especially deoxynucleosides, The 8-hydroxy-2′-deoxyguanosine

(8-OHdG) and/or its tautomeric 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) have been proved

important mutagenic adducts to DNA and therefore potential biomarkers of carcinogenesis. Mutations

of 8-oxodG involve a GC → TA transversion [112,113]. Also, ROS and RNS with their oxidative

potential may initiate carcinogenesis by attacking DNA nucleobases causing certain changes in

oncogenes and tumour suppressor genes [114]. Experimental results showed that HO· generates DNA

phenotypes with various metastatic potential that are likely to contribute to the diverse physiological

properties and heterogeneity characteristic of metastatic cell population [115].

Clinical and epidemiological evidence from animal studies showed that consumption of animal

fats, strongly influence the incidence of mammary and sigmoid colon cancers, through lipid

peroxidation [116–119]. High fat diets cause proliferation of rat hepatic peroxisomes and an increase

of peroxisomal and mitochondrial enzymes involved in fatty acid β-oxidation [120]. These changes

and other fat metabolites, such as unsaturated aldehydes, may play a critical role in oxidative DNA

Int. J. Environ. Res. Public Health 2013, 10 3894

damage and the liberation of low levels of H2O2, supporting the suggestion that direct DNA damage

may be the mode of carcinogenic action of peroxisome proliferators [121,122]. Lipid peroxidation

generates a complex variety of reactive electrophilic products and free radicals, that react with proteins

and DNA [123,124].

ROS and RNS can react with cellular membrane phospholipids generating lipoperoxide radicals

(LOO·) and toxic aldehydes (malondialdehyde, MDA) that can alter membrane permeability and

microcirculation. Also, they can activate nuclear factors leading to other proi-nflammatory agents.

Malondialdehyde is a naturally occurring product of lipid peroxidation and prostaglandin biosynthesis,

which is mutagenic and carcinogenic compound. MDA reacts with DNA to form adducts to

nucleobases deoxyguanosine and deoxyadenosine [125]. MDA was shown to be carcinogenic in mice

and tumours arose in a very short time after administration [126]. Several other adlehydes, including

α,β-unsaturated aldehydes have been proved mutagenic in Salmonella typhimurium [127,128]. Lipid

peroxidation, inflammation produce MDA which reacts with nucleobases to form multiple adducts

with mutagenic potential [129–131].

6. Telomere Shortening and Carcinogenesis. Epigenetic Effects Mediated by ROS. (Modulation

of Gene Expression and Activation of Transcription Factors)

Telomere is a region of repetitive nucleotide sequences at each end of a chromatid protecting the

end of the chromosome from deterioration or from fusion with neighboring chromosomes of most

eukaryotic organisms, regulating many crucial cellular functions in multicellular organisms such as

ageing and cancer [132]. Telomere repeats are most often maintained by a specialized reverse

transcriptase called telomerase. The interplay among telomeric repeats, telomerase and telomere-binding

proteins governs a wide range of cellular processes, including chromosomal stability, gene expression

and cell replicative life span [133,134]. Telomere are sensitive to shortening due to oxidative DNA

damage can be very important for carcinogenesis [135,136].

Damaged nucleobases due to ROS oxidative stress can accumulate over the life span contributing

significantly to the senescence of an organism. It has been found that senescent cells contain 30%

more oxidatively modified guanines in their DNA and four times more 8-oxodG bases, a well studied

biomarker of oxidative damage by ROS produced mainly from exposure to mineral fibres, dusts,

particulate matter and heavy metals [137,138]. When human telomeres become very short they are no

longer able to protect chromosome ends, particularly in the setting of loss of function of the

retinoblastoma (pRB)) and p53 tumour-suppressor pathways. The resulting genomic instability leads

to chromosomal breaks and fusion that permit the acquisition of further genetic changes and mutations.

Genome instability is known as a hallmark of most human cancers. Scientists were arguing that collapse in

telomere function can explain a significant portion of genetic instability in tumours [139–141]. Recent

findings suggest that telomere maintenance might not be an obligate requirement for initial tumour

formation in some settings and that telomerase (reverse transcriptase that provides the template for the

telomere synthesis reaction) activation contributes to tumour formation independently of its role in

maintaining telomere length [142].

Ageing is known from various studies that increases the susceptibility of tissues to carcinogenesis

by several mechanisms: (i) tissue accumulation of cells in late stage of carcinogenesis; (ii) alterations

Int. J. Environ. Res. Public Health 2013, 10 3895

in homeostasis in immune and endocrine systems; (iii) telomere instability because of oxidative

shortening linking ageing with increased cancer risk. There is strong experimental evidence supporting

the relevance of replicative senescence of human cells and telomere biology to human cancer [143].

Studies showed that exposure to airborne PM (in urban settings) and tobacco smoke are important

factors in telomere shortening (or erosion) in humans [144–146].

The epigenetic effects caused by ROS and RNS, especially the adaptive responses induced in

mammalian cells by the upregulation of stress-response genes, encode enzymatic antioxidant defence

mechanisms. Low or transient ROS concentrations increase cell proliferation, through altered

expression of growth factors and proto-oncogenes, whereas high ROS production lead to induction of

apoptosis. ROS can induce alteration of gene expression that can occur through modulation of a host

of signaling pathways, such as cAMP-mediated cascades, calcium-calmodulin pathways and

intracellular signal transducers of nitric oxide (NO·) [147].

ROS and other oxidants can stimulate signal transduction pathways and lead to activation of key

transcription factors such as Nrf2 and NF-κB. The resultant altered gene expression patterns evoked

can contribute to the carcinogenesis process. Recent evidence demonstrates an association between a

number of single nucleotide polymorphisms (SNPs) in oxidative DNA repair genes and antioxidant

genes with human cancer susceptibility. These pathways regulate cellular migration, death,

proliferation and survival, thus aberrant activation can paly a role in potential mechanisms of

carcinogenesis [148]. Changes in epigenetic processes, such DNA methylation that leads to gene

silencing without altering the DNA sequence, occur with air pollutant exposure, especially by global

and gene-specific methylation changes. Respiratory cell line and animal models demonstrate distinct

gene expression signatures in the transcriptome, arising from exposure to particulate matter or ozone.

Particulate matter and other environmental pollutants alter expression of microRNA, which are short

non-coding RNA that regulate gene expression [149]. Ageing also affects the epigenetic processes and

mechanisms of carcinogenesis as well the oncogene expression and inevitably the spread of cancer and

metastasis [150,151].

Careful study of genomic responses will improve the scientific understanding of mechanisms of

lung injury from air pollution and will enable future clinical testing of interventions against toxic

effects of air pollutants. Workplace exposures, such as tobacco smoke, particulates, diesel exhaust,

polyaromatic hydrocarbons, ozone, and endotoxin, among others, enhance expression of inflammatory

cytokines and allergic phenotypes by epigenetic means [152]. The transcription factors that are

activated have been under the influence of cellular oxidants. ROS appear to influence selective

activation of these transcription factors and in this way may explain the effects on cell death or cell

proliferation in mechanisms of carcinogenesis, through exposure to ROS and oxidative stress. In this

respect, scientists believe that inhibition of transcription factors must be targets for new anticancer

drugs [153].

The most important transcription factors, correlated to activation by oxidants and implicated in the

mechanisms of carcinogenesis are described briefly below. Most of these transcription factors are

activated by particulate matter, tobacco smoke and mineral fibers that are generating ROS and other

reactive oxidant species.

The nuclear factor erythroid-derived 2 (Nrf2), which upon activation results in transcriptional

expression of a broad spectrum of enzymes involved in xenobiotic detoxification, antioxidant response

Int. J. Environ. Res. Public Health 2013, 10 3896

and proteome maintenance. Experiments with mice showed that they are more sensitive to the hepatic,

pulmonary, ovarian, and neurotoxic consequences of acute exposures to environmental pollutants,

inflammatory stresses and chronic exposures to cigarette smoke and other carcinogens [154]. Studies

showed that the Nrf2 antioxidant and cellular detoxification program represents a previously

unappreciated mediator of oncogenesis [155]. This factor has dual roles in carcinogenesis. In response

to oxidative stress, the transcription factor NF-E2-related factor 2 (Nrf2) controls the fate of cells

through transcriptional upregulation of antioxidant response element-bearing genes, including those

encoding endogenous antioxidants, phase II detoxifying enzymes, and transporters. Expression of the

Nrf2-dependent proteins is critical for ameliorating or eliminating toxicants/carcinogens to maintain

cellular redox homeostasis [156].

The activation protein-1 (AP-1) contributes to basal gene expression in biological systems. ROS

can activate AP-1 through several mechanisms. The effect of AP-1 activation is an increased cell

proliferation due to increased expression of growth stimulatory genes such as cyclin D1. and

suppression of the protein p21waf. Studies showed that AP-1 and NF-kappaB, inducible by tumour

promoters of oxidative stimuli, show differential protein levels or activation in response to tumour

promoters in JB6 cells. Researchers suggest that as long as oxidative events regulate AP-1 and

NF-kappaB transactivation, these oxidative events can be important molecular targets for cancer

prevention [157,158].

The Nuclear Factor-kappaB (NF-kB) (NF-kappa-light-chain enhancer of activated B cells), is

expressed and participates in a wide range of biological processes, such as cell survival,

differentiation, inflammation and growth [159]. NF-kB activation has been linked to a wide spectrum

of extracellualr stimuli and oxidants and subsequent involvement in the carcinogenic process through

promotion of angiogenesis and tumour cell invasion and metastasis [160,161].

Another transcription factor is HIF-1 (a heterodimeric transcription factor, Hypoxia-inducible

factor-1) that has been implicated in ROS-induced carcinogenesis in a variety of human

cancers [162,163]. The response to hypoxia in human cells is mainly regulated by hypoxia-inducible

factors or HIFs which orchestrate signaling events leading to angiogenesis and tumorigenesis.

A recent review underlined the molecular mechanisms for tumour hypoxia and their pro-tumour

contribution to various biochemical changes leading to tumour cell metastasis [164].

Scientists experimented for years with the p53, that is a well known tumour suppressor gene. The

p53 regulates cellular antioxidant defence and energy metabolism. The current theory suggest that

neoplastic transformation consists of multistep accumulations of adverse genetic and epigenetic events.

The p53 is a transcription factor that regulates cellular response to diverse forms of stress through a

complex network which monitors genome integrity and cell homeostasis. It is generally accepted that

p53 is a component in biochemical pathways central to human carcinogenesis. Study of p53 has come

to the forefront of cancer research, and detection of its abnormalities during the development of tumors

may have diagnostic, prognostic, and therapeutic implications [165]. A recent review described the

tumor suppressor protein p53 which is susceptible to ROS and controls a wide variety of target genes

and regulates numerous cellular functions in response to stresses that lead to genomic instability [166].

Another review discussed the multiple functions of p53 and how these correlate between cancer and

neurodegeneration. Loss of function in p53 is usually associated with many common human cancers

and p53 gene is mutated in almost half of all human cancers. There is a scientific hypothesis that the

Int. J. Environ. Res. Public Health 2013, 10 3897

p53 conformational state is affected by ROS/RNS which may not be only a mere consequence of

oxidative stress, but a fine gene transcription mechanism allowing specific adaptive responses. [167].

Recently, researchers discovered that glutaminase 2 (GLS2) is a p53 target. Phosphate-activated

mitochondrial glutaminase (GLS2), and its expression is induced in response to DNA damage or

oxidative stress in a p53 dependent manner. The GLS2 is a key enzyme in conversion of glutamine to

glutamate and therefore a regulator of the synthesis of antioxidant glutathione (GSH). Increased

concentration of GLS2 facilitates glutamide metabolism and lowers intracellular levels of ROS,

resulting in an overall decrease in DNA damage as determined by 8-hydroxy-deoxyguanosine

(8-OHdG) in both normal and stressed cells. This result provides evidence for a unique role for p53,

linking glutamine metabolism, energy and ROS homeostasis, that may contribute to p53 tumor

suppressor function [168].

7. Conclusions

In this review we presented the most important and recent studies concerning the role of ROS, RNS

and other oxidants in the biochemical pathways of oxidative stress, pulmonary inflammation and the

initiation of lung carcinogenesis. The human lungs are exposed continuously to air pollution oxidants

in addition to endogenously generated ROS and RNS which are involved in physiological biochemical

mechanisms and normal cellular signaling pathways. This review highlights the important role of

inhalable particulate matter, mineral fibres, dusts, cigarette smoke and ozone in the generation of ROS,

RNS, lipid radicals and other oxidants. In the last decade scientific evidence is available that supports

the importance of oxidative stress and its correlation with increased incidence of malignant respiratory

diseases due to inflammation, activation of transcriptional factors and DNA damage. Although all

aerobic organisms are protected by enzymatic and non enzymatic antioxidant defences, an imbalance

of prooxidants and antioxidants in the cellular environment can result to oxidative stress mechanisms,

inflammation, carcinogenesis and ageing. During inflammation, enhanced ROS production induce

DNA damage, inhibition of apoptosis, and activation of protooncogenes by initiating signal

transduction pathways. Inflammatory cells are particularly effective in generating ROS and other

reactive species, thus increasing oxidative damage and promoting mechanisms of carcinogenesis.

Particularly DNA damage mediated by oxidative stress has been found by numerous studies to play an

important role in the various stages of initiation, promotion and progression of cancer. Lipid

peroxidation of cellular membranes and accumulation of mutagenic products in DNA can contribute to

mechanisms of carcinogenesis, while telomere shortening through oxidative stress and senescence

increases cancer risk.

Conflicts of Interest

The authors declare no conflict of interest.

Int. J. Environ. Res. Public Health 2013, 10 3898

References

1. Aust, A.E.; Balla, J.C.; Hu, A.A.; Lighty, J.S.; Smith, K.R.; Straccia, A.M.; Veranth, J.M.;

Young, W.C. Particle characteristics responsible for effects on human lung epithelial cells.

Res. Rep. Health Effects Inst. 2002, 5, 1–65.

2. Nagai, H.; Toyokuni, S. Biopersistent fiber-induced inflammation and carcinogenesis: Lessons

learned from asbestos toward safety of fibrous nanomaterials. Arch. Biochem. Biophys. 2010,

502, 1–7.

3. Chuang, H.C.; Fan, C.W.; Chen, K.Y.; Chang-Chien, G.P.; Chan, C.C. Vasoactive alteration and

inflammation induced by polycyclic aromatic hydrocarbons and trace metals of vehicle exhaust

particles. Toxicol. Lett. 2012, 214, 131–136.

4. Strak, M.; Janssen, N.A.; Godri, K.J.; Gosens, I.; Mudway, I.S.; Cassee, F.R.; Lebret, E.;

Kelly, F.J.; Harrison, R.M.; Brunekreef, B.; et al. Respiratory health effects of airborne

particulate matter: The role of particle size, composition, and oxidative potential-the RAPTES

project. Environ. Health Perspect. 2012, 120, 1183–1189.

5. Gardi, C.; Valacchi, G. Cigarette smoke and ozone effect on murine inflammatory responses.

Ann. N.Y. Acad. Sci. 2012, 1259, 104–111.

6. Sangani, R.G.; Ghio, A.J. Lung injury after cigarette smoking is particle related. Int. J. Chron.

Obstruct. Pulmon. Dis. 2011, 6, 191–198.

7. Pryor, W.A. Cigarette smoke radicals and the role of free radicals in chemical carcinogenicity.

Environ. Health Perspect. 1997, 105, 875

8. Hannan, M.A.; Recio, L.; Deluca, P.P.; Enoch, H. Co-mutagenic effects of 2-aminoanthracene

and cigarette smoke condensate on smoker’s urine in the Ames Salmonella assay system. Cancer

Lett. 1981, 13, 203–212.

9. Møller, P.; Folkmann, J.K.; Forchhammer, L.; Bräuner, E.V.; Danielsen, P.H.; Risom, L.;

Loft, S. Air pollution, oxidative damage to DNA, and carcinogenesis. Cancer Lett. 2008, 266,

84–97.

10. Risom, L.; Møller, P.; Loft, S. Oxidative stress-induced DNA damage by particulate air

pollution. Mutat. Res. 2005, 592, 119–137.

11. Squadrito, G.L.; Cueto, R.; Dellinger, B.; Pryor, W.A. Quinoid redox cycling as a mechanism for

sustained free radical generation by inhaled airborne particulate matter. Free Radic. Biol. Med.

2001, 31, 1132–1138.

12. Ohyama, M.; Otake, T.; Adachi, S.; Kobayashi, T.; Morinaga, K. A comparison of the

production of reactive oxygen species by suspended particulate matter and diesel exhaust

particles with macrophages. Inhal. Toxicol. 2007, 19, 157–160.

13. Valavanidis, A.; Fiotakis, K.; Vlachogianni, T. Airborne particulate matter and human health:

Toxicological assessment and importance of size and composition of particles for oxidative

damage and carcinogenic mechanisms. J. Environ. Sci. Health C Environ. Carcinog. Ecotoxicol.

Rev. 2008, 26, 339–362.

14. Wu, L.L.; Chiou, C.C.; Chang, P.Y.; Wu, J.T. Urinary 8-OHdG a marker of oxidative stress to

DNA and a risk factor for cancer, atheroschlerosis and diabetics. Clin. Chim. Acta 2004, 339, 1–9.

Int. J. Environ. Res. Public Health 2013, 10 3899

15. Pilger, A.; Rüdiger, H.W. 8-Hydroxy-2′-deoxyguanosine as a marker of oxidative DNA damage

related to occupational and environmental exposures. Int. Arch. Occup. Environ. Health 2006,

80, 1–15.

16. Evans, M.D.; Dizdaroglou, M.; Cooke, M.S. Oxidative DNA damage and disease: Induction,

repair and significance. Mutat. Res. 2004, 567, 1–61.

17. Sunil, V.R.; Kinal, J.; Vayas, K.J.; Massa, C.B.; Andrew, J.; Gow, A.J.; Jeffrey, D.; Laskin, J.D.;

Laskin, D.L. Ozone-induced Injury and oxidative stress in bronchiolar epithelium is associated

with altered pulmonary mechanics. Toxicol. Sci. 2013, 33, 309–319.

18. Sunil, V.R.; Patel-Vayas, K.; Shen, J.; Laskin, J.D.; Laskin, D.L. Classical and alternative

macrophage activation in the lung following ozone-induced oxidative stress. Toxicol. Appl.

Pharmacol. 2012, 263, 195–202.

19. Yu, M.; Zheng, X.; Witschi, H.; Pinkerton, K.E. The role of interleukin-6 in pulmonary

inflammation and injury induced by exposure to environmental pollutants. Toxicol. Sci. 2002, 68,

488–497.

20. Droge, W. Free radicals in the physiological control of cell function. Physiol. Rev. 2002, 82,

47–95.

21. Halliwel, B.; Gutteridge, J.M.C. Free Radicals in Biology and Medicine; Oxford University

Press: New York, NY, USA, 1999.

22. Thannickal, V.J.; Fanburg, B.L. Reactive oxygen species in cell signaling. Am. J. Physiol. Lung

Cell Mol. Physiol. 2000, 279, L1005–L1028.

23. Brookes, P.S.; Levonen, A.L.; Shiva, S.; Sarti, P.; Darley-Usmar, V.M. Mitochondria:

Regulators of signal transduction by reactive oxygen and nitrogen species. Free Radic. Biol.

Med. 2002, 33, 755–764.

24. Nathan, C. Specificity of a third kind: Reactive oxygen and nitrogen intermediates in cell

signaling. J. Clin. Invest. 2003, 111, 769–778.

25. Circu, M.L.; Aw, T.Y. Reactive oxygen species, cellular redox systems, and apoptosis.

Free Radic. Biol. Med. 2010, 48, 749–762.

26. Matés, J.M.; Segura, J.A.; Alonso, F.J.; Márquez, J. Oxidative stress in apoptosis and cancer:

An update. Arch. Toxicol. 2012, 86, 1649–1665.

27. Sosa, V.; Moliné, T.; Somoza, R.; Paciucci, R.; Kondoh, H.; Leonart, M.E. Oxidative stress and

cancer: An overview. Ag. Res. Rev. 2013, 12, 376–390.

28. Valko, M.; Izakovic, M.; Maur, M.; Rhodes, C.J.; Telser, J. Role of oxygen radicals in DNA

damage and cancer incidence. Mol. Cell Biochem. 2004, 266, 37–56.

29. Bartsch, H.; Nair, J. Chronic inflammation and oxidative stress in the genesis and perpetuation of

cancer: Role of lipid peroxidation, DNA damage, and repair. Langenbecks Arch. Surg. 2006,

391, 499–510.

30. Valko, M.; Leibfritz, D.; Moncol, J.; Cronin, M.T.D.; Mazur, M.; Tesler, J. Free radicals and

antioxidants in normal physiological function and human disease. Int. J. Biochem. Cell Biol.

2007, 39, 44–84.

31. Halliwell, B.; Gutteridge, J.M.C. The antioxidants of extracellular fluids. Arch Biochem.

Biophys. 1990, 280, 1–8.

32. Sena, L.A.; Chandel, N.S. Physiological roles of mitochondrial reactive oxygen species.

Mol. Cell. 2012, 48, 158–167.

Int. J. Environ. Res. Public Health 2013, 10 3900

33. Ottavio, F.G.; Handy, D.E.; Loscalzo, J. Redox regulation in the extracellular environment.

Circ. J. 2008, 72, 1–16.

34. Cerutti, P.A. Prooxidant states and tumor promotion. Science 1985, 227, 375–380.

35. Dreher, D.; Junod, A.F. Role of oxygen free radicals in cancer development. Eur. J. Cancer

1996, 32A, 30–38.

36. Toyokuni, S. Molecular mechanisms of oxidative stress-induced carcinogenesis: From

epidemiology to oxygenomics. Int. Union Biochem. Mol. Biol. (IUBMB) Life 2008, 60, 441–447.

37. Hahn, W.C.; Weinberg, R.A. Modeling the molecular circuitry of cancer. Nat. Rev. Cancer 2002,

2, 331–341.

38. Weinberg, R.A. The Biology of Cancer; Garland Science (Taylor & Francis Group): New York,

NY, USA, 2006.

39. Ziech, D.; Franco, R.; Pappa, A.; Panayiotidis, M.I. Reactive oxygen speciers (ROS)-induced

genetic and epigenetic alterations in human carcinogenesis. Mutat. Res. 2011, 711, 167–173.

40. Azad, N.; Rojanasakul, Y.; Vallyathan, V. Inflammation and lung cancer: Roles of reactive

oxygen/nitrogen species. J. Toxicol. Environ. Health B Crit. Rev. 2008, 11, 1–15.

41. Fitzpatrick, F.A. Inflammation, carcinogenesis and cancer. Int. Immunolpharmacol. 2001, 1,

1651–1667.

42. Coussens, L.M.; Werb, Z. Inflammation and cancer. Nature 2002, 420, 860–867.

43. Federico, A.; Morgillo, F.; Tuccillo, C.; Ciardiello, F.; Loguercio, C. Chronic inflammation and

oxidative stress in human carcinogenesis. Int. J. Cancer 2007, 121, 2381–2386.

44. Kundu, J.K.; Surh, Y.J. Inflammation: Gearing the journey to cancer. Mutat. Res. 2008, 659,

15–30.

45. Lazennes, G.; Richmond, A. Chemokines and chemokine receptors: New insights into

cancer-related inflammation. Trends Mol. Med. 2010, 16, 133–144.

46. Rodriguez-Vita, J.; Lawrence, T. The resolution of inflammation and cancer. Cytokine Growth

Factor Rev. 2010, 21, 61–65.

47. Truss, M.A.; Kensler, T.W. An overview of the relationship between oxidative stress and

chemical carcinogenesis. Free Radic. Biol. Med. 1991, 10, 201–209.

48. Porta, C.; Larghi, P.; Rimoldi, M.; Totaro, M.G.; Allavena, P.; Mantovani, A.; Sica, A. Cellular

and molecular pathways linking inflammation to cancer. Immunobiology 2009, 214, 761–777.

49. Jackson, J.R.; Seed, M.P.; Kircher, C.H.; Willoughby, D.A.; Winkler, J.D. The codependence of

angiogenesis and chronic inflammation. FASEB J. 1997, 11, 457–465.

50. Costa, C.; Incio, J.; Soaes, R. Angiogenesis and chronic inflammation: Cause of consequence?

Angiogenesis 2007, 10, 149–166.

51. Dalgeish, A.G.; O’Byrne, K. Inflammation and cancer: The role of the immune response and

angiogenesis. Cancer Treat. Res. 2006, 130, 1–38.

52. Allavena, P.; Sica, A.; Sollinas, G.; Porta, G.; Mantovani, A. The inflammatory micro-environment

in tumor progression: The role of tumor-associated macrophages. Crit. Rev. Oncol. Hematol.

2008, 66, 1–9.

53. Benelli, R.; Lorusco, G.; Albini, A.; Nooman, D.M. Cytokines and chemokines as regulators of

angiogenesis in health and disease. Curr. Pharm. Des. 2006, 12, 3101–3115.

Int. J. Environ. Res. Public Health 2013, 10 3901

54. Donaldson, K.; Stone, V.; Borm, P.J.; Jimenez, L.A.; Gilmour, P.S.; Schins, R.P.;

Knaapen, A.M.; Rahman, I.; Faux, S.P.; Brown, D.M.; et al. Oxidative stress and calcium

signaling in the adverse effects of environmental particles (PM10). Free Radic. Biol. Med. 2003,

34, 1369–1382.

55. Lim, H.B.; Ichinose, T.; Miyabara, Y.; Takano, H.; Kumagai, Y.; Shimojyo, N.; Devalia, J.L.;

Sagai, M. Involvement of superoxide and nitric oxide on airway inflammation and

hyperresponsiveness induced by diesel exhaust particles in mice. Free Radic. Biol. Med. 1998,

25, 635–644.

56. Vendramini-Costa, D.B.; Carvalho, J.E. Molecular link mechanisms between inflammation and

cancer. Curr. Pharm. Des. 2012, 18, 3831–3852.

57. Gurgueira, S.A.; Lawrence, J.; Coull, B.; Murthy, G.G.; Gonzalez-Flecha, B. Rapid increases in

the steady-state concentration of reactive oxygen species in the lungs and heart after particulate

air pollution inhalation. Environ. Health Perspect. 2002, 110, 749–755.

58. Li, N.; Xia, T.; Nel, A.E. The role of oxidative stress in ambient particulate matter-induced lung

diseases and its implications in the toxicity of engineered nanoparticles. Free Radic. Biol. Med.

2008, 44, 1689–1699.

59. Xiao, G.G.; Wang, M.; Li, N.; Loo, J.A.; Nel, A.E. Use of proteomics to demonstrate a

hierarchical oxidative stress response to diesel exhaust particle chemicals in a macrophage cell

line. J. Biol. Chem. 2003, 278, 50781–50790.

60. Sies, H. Oxidative Stress: Introductory Remarks. In Oxidative Stress; Sies, H., Ed.; Academic

Press: London, UK, 1985; pp. 1–8.

61. Foyer, C.H. Redox homeostasis and antioxidant signaling: A metabolic interface between stress

perception and physiological responses. Plant Cell 2006, 17, 1866–1875.

62. Ghio, A.J.; Carraway, M.S.; Madden, M.C. Composition of air pollution particles and oxidative

stress in cells, tissues, and living systems. J. Toxicol. Environ. Health B Crit. Rev. 2012, 15,

1–21.

63. Rhoden, C.R.; Wellenius, G.A.; Ghelfi, E, Lawrence, J.; Gonzalez-Flecha, B. PM-induced

cardiac oxidative stress and dysfunction are mediated by autonomic stimulation. Biochim.

Biophys. Acta 2005, 1725, 305–313.

64. Terzano, C.; Di Stefano, F.; Conti, V.; Graziani, E.; Petroianni, A. Air pollution ultrafine

particles: Toxicity beyond the lung. Eur. Rev. Med. Pharmacol. Sci. 2010, 14, 809–821.

65. Knaapen, A.M.; Shi, T.; Borm, P.J.; Schins, R.P. Soluble metals as well as the insoluble particle

fraction are involved in cellular DNA damage induced by particulate matter. Mol. Cell Biochem.

2002, 234–235, 317–326.

66. Shi, T.; Knaapen, A.M.; Begerow, J.; Birmili, W.; Borm, P.J.; Schin, R.P. Temporal variation of

hydroxyl radical generation and 8-hydroxy-2′-deoxyguanosine formation by coarse and fine

particulate matter. Occup. Environ. Med. 2003, 60, 315–321.

67. Valavanidis, A.; Fiotakis, K.; Vlachogianni, T. The Role of Stable Free Radicals, Metals and

PAHs of Airborne Particulate Matter in Mechanisms o Oxidative Stress and Carcinogenesis.

In Urban Airborne Particulate Matter; Zereini, F., Wiseman, C.L.S., Eds.; Springer-Verlag:

Berlin, Heidelberg, Germany, 2010; pp. 411–429.

Int. J. Environ. Res. Public Health 2013, 10 3902

68. Shi, T.; Duffin, R.; Borm, P.J.; Li, H.; Weishaupt, C.; Schins, R.P. Hydroxyl-radical-dependent

DNA damage by ambient particulate matter from contrasting sampling locations. Environ. Res.

2006, 1, 18–24.

69. Donaldson, K.; Brown, D.M.; Mitchell, C.; Dineva, M.; Beswick, P.H.; Gilmour, P.;

MacNee, W. Free radical activity of PM10: Iron-mediated generation of hydroxyl radicals.

Environ. Health Perspect. 1997, 105, 1285–1289.

70. Dellinger, B.; Pryor, W.A.; Cueto, R.; Squadrito, G.L.; Hedge, V.; Deutsch, W.A. Role of free

radicals in the toxicity of airborne particulate matter. Chem. Res. Toxicol. 2001, 14, 1371–1377.

71. Penning, T.M.; Burczynski, M.E.; Hung, C.F.; McCoull, K.D.; Palackal, N.T.; Tsuruda, L.S.

Dihydrodiol dehydrogenases and polycyclic aromatic hydrocarbon activation: Generation of

reactive and redox active o-quinones. Chem. Res. Toxicol. 1999, 12, 1–18.

72. Park, J.H.; Troxel, A.B.; Harvey, R.G.; Penning, T.M. Polycyclic aromatic hydrocarbon (PAH)

o-quinones produced by the aldo-keto-reductases (AKRs) generate abasic sites, oxidized

pyrimidines, and 8-oxo-dGuo via reactive oxygen species. Chem. Res. Toxicol. 2006, 19,

719–728.

73. Valavanidis, A.; Fiotakis, K.; Bakeas, E.; Vlahogianni, T. Electron paramagnetic resonance study

of the generation of reactive oxygen species catalysed by transition metals and quinoid redox

cycling by inhalable ambient particulate matter. Redox Rep. 2005, 10, 37–51.

74. Rubin, H. Synergistic mechanisms in carcinogenesis by polycyclic aromatic hydrocarbons and

by tobacco smoke: A bio-historical perspective with updates. Carcinogenesis 2001, 22, 1903–

1930.

75. Yoshie, Y.; Ohshima, H. Synergistic induction of DNA strand breakage by cigarette tar and nitric

oxide. Carcinogenesis 1997, 18, 1359–1363.

76. Zhou, Y.M.; Zhong, C.Y.; Kennedy, I.M.; Leppert, V.J.; Pinkerton, K.E. Oxidative stress and

NFkappaB activation in the lungs of rats: A synergistic interaction between soot and iron

particles. Toxicol. Appl. Pharmacol. 2003, 190, 157–169.

77. Stone, V.; Wilson, M.R.; Lightbody, J.; Donaldson, K. Investigating the potential for interaction

between the components of PM(10). Environ. Health Prev. Med. 2003, 7, 246–253.

78. Valavanidis, A.; Loridas, S.; Vlahogianni, T.; Fiotakis, K. Influence of ozone on traffic-related

particulate matter on the generation of hydroxyl radicals through a heterogeneous synergistic

effect. J. Hazard Mater. 2009, 162, 886–892.

79. Bouthillier, L.; Vincent, R.; Goegan, P.; Adamson, I.Y.; Bjarnason, S.; Stewart, M.; Guénette, J.;

Potvin, M.; Kumarathasan, P. Acute effects of inhaled urban particles and ozone: Lung

morphology, macrophage activity, and plasma endothelin-1. Am. J. Pathol. 1998, 153,

1873–1884.

80. Valavanidis, A.; Vlachogianni, T.; Fiotakis, K. Tobacco smoke: Involvement of reactive oxygen

species and stable free radicals in mechanisms of oxidative damage, carcinogenesis and

synergistic effects with other respirable particles. Int. J. Environ. Res. Public Health 2009, 6,

445–462.

81. Morimoto, Y.; Kido, M.; Tanaka, I.; Fujino, A.; Higashi, T.; Yokosaki, Y. Synergistic effects of

mineral fibres and cigarette smoke on the production of tumour necrosis factor by alveolar

macrophages of rats. Br. J. Ind. Med. 1993, 50, 955–960.

Int. J. Environ. Res. Public Health 2013, 10 3903

82. Danielsent, P.H.; Mollert, P.; Jensen, K.A.; Sharma, A.K.; Wallin, H.; Bossi, R.; Autrup, H.;

Mølhave, L.; Ravanat, J.L.; Briedé, J.J.; et al. Oxidative stress, DNA damage, and inflammation

by ambient air and wood smoke particulate matter in human A549 and THP-1 cell lines.

Chem. Res. Toxicol. 2011, 24, 168–184.

83. DosReis, G.A.; Borges, V.M. Role of Fas-ligand induced apoptosis in pulmonary inflammation

and injury. Curr. Drug Targets Inflamm. Allergy 2003, 2, 161–167.

84. Xia, T.; Kovochich, M.; Nel, A.E. Impairment of mitochondrial function by particulate matter

(PM) and their toxic components: implications for PM-induced cardiovascular and lung diseases.

Front Biosci. 2007, 12, 1238–1246.

85. Martin, L.D.; Krunkosky, T.M.; Dye, J.A.; Fischer, B.M.; Jiang, N.F.; Rochelle, L.G.;

Akley, N.J.; Dreher, K.L.; Adler, K.B. The role of reactive oxygen and nitrogen species in the

response of airway epithelium to particulates. Environ. Health Perspect. 1997, 105, 1301–1307.

86. Rosanna, D.P.; Salvatore, C. Reactive oxygen species, inflammation, and lung disease. Curr.

Pharm. Des. 2012, 18, 3889–3900.

87. Knaapen, A.M.; Gungor, N.; Schins, R.P.; Borm, P.J.; van Schooten, F.J. Neutrophils and

respiratory tract DNA damage and mutagenesis: A review. Mutagenesis 2006, 21, 225–236.

88. Taniyama, Y.; Griendling, K.K. Reactive oxygen species in the vasculature: Molecular and

cellular mechanisms. Hypertension 2003, 42, 1075–1081.

89. Storr, S.J.; Woolston, C.M.; Zhang, Y.; Martin, S.G. Redox environment, free radicals, and

oxidative DNA damage. Antioxid. Redox Signal. 2013, 18, 2399–2408.

90. Valavanidis, A.; Vlachogianni, T.; Fiotakis, C. 8-Hydroxy-2′-deoxyguanosine (8-OHdG):

A critical biomarker of oxidative stress and carcinogenesis. J. Environ. Sci. Health C-Envir.

2009, 27, 1–20.

91. Van Berlo, D.; Hullmann, M.; Schins, R.P.F. Toxicology of Ambient Particulate Matter.

In Experientia Supplementum Molecular, Clinical and Environmental Toxicology; Luch, A., Ed.;

Springer Basel AG: Heidelberg, Germany, 2012; Volume 3, pp. 165–218.

92. Jena, N.R. DNA damage by reactive species: Mechanisms, mutation and repair. J. Biosci. 2012,

37, 503–517.

93. Beckman, K.B.; Ames, B.N. Oxidative decay of DNA. J. Biol. Chem. 1997, 272, 217–225.

94. Dizdaroglu, M. Oxidatively induced DNA damage: Mechanisms, repair and disease. Cancer Lett.

2012, 327, 26–47.

95. Dizdaroglu, M.; Jaruga, P. Mechanisms of free radical-induced damage to DNA. Free Radic.

Res. 2012, 46, 382–419.

96. Park, C.B.; Larsson, N.G. Mitochondrial DNA mutations in disease and aging. J. Cell Biol. 2011,

193, 809–818.

97. Beckman, K.B.; Ames, B.N. Endogenous oxidative damage of mtDNA. Mutat. Res. 1999, 424,

51–58.

98. Klaunig, J.E.; Kamendulis, L.M. The role of oxidative stress in carcinogenesis. Review. Annu.

Rev. Pharmacol. Toxicol. 2004, 44, 239–267.

99. Berneburg, M.; Kamenisch, Y.; Krutmann, J. Repair of mitochondrial DNA in aging and

carcinogenesis. Photochem. Photobiol. Sci. 2006, 5, 190–198.

Int. J. Environ. Res. Public Health 2013, 10 3904

100. Ralph, S.J.; Rodríguez-Enríquez, S.; Neuzil, J.; Saavedra, E.; Moreno-Sánchez, R. The causes of

cancer revisited: ―Mitochondrial malignancy‖ and ROS-induced oncogenic transformation—

Why mitochondria are targets for cancer therapy. Mol. Aspects Med. 2010, 31, 145–170.

101. Møller, P.; Jacobsen, N.R.; Folkmann, J.K.; Danielsen, P.H.; Mikkelsen, L.; Hemmingsen, J.G.;

Vesterdal, L.K.; Forchhammer, L.; Wallin, H.; Loft, S. Role of oxidative damage in toxicity of

particulates. Free Radic. Res. 2010, 44, 1–46.

102. Mates, J.M.; Segura, J.A.; Alonso, F.J.; Marquez, J. Intercellular redox status and oxidative

stress: Implications for cell proliferation, apoptosis, and carcinogenesis. Arch. Toxicol. 2008, 82,

273–299.

103. Paz-Elizur, T.; Sevilya, Z.; Leitner-Dagan, Y.; Elinger, D.; Roisman, L.C.; Livneh, Z. DNA

repair of oxidative DNA damage in human carcinogenesis: Potential application for cancer risk

assessment and prevention. Cancer Lett. 2008, 266, 60–72.

104. Soriani, M.; Luscher, P.; Tyrrell, R.M. Direct and indirect modulation of ornithine decarboxylase

and cyclooxygenase by UVB radiation in human skin cells. Carcinogenesis 1999, 20, 727–732.

105. Zhao, Y.; Xue, Y.; Oberley, T.D.; Kiningham, K.K.; Lin, S.M.; Yen, H.C.; Majima, H.;

Hines, J.; St Clair, D. Overexpression of manganese superoxide dismutase supresses tumor

formation by modulation of activator protein-1 signaling in the multistage skin carcinogenesis

model. Cancer Res. 2001, 61, 6082–6088.

106. Briede, J.J.; van Delft, J.M.; de Kok, T.M.; van Herwijnen, M.H.; Maas, L.M.; Gottschalk, R.W.;

Kleinjans, J.C. Global gene expression analysis reveals differences in cellular response to

hydroxyl- and superoxide anion radical-induced oxidative stress in caco-2 cells. Toxicol. Sci.

2010, 114, 193–203.

107. Shi, H.; Shi, X.; Liu, K.J. Oxidative mechanism of arsenic toxicity and carcinogenesis. Mol. Cell

Biochem. 2004, 255, 62–78.

108. Salnikow, K.; Zhitkovich, A. Genetic and epigenetic mechanisms in metal carcinogenesis and

cocarcinogenesis: Nickel, arsenic, and chromium. Chem. Res. Toxicol. 2008, 21, 28–44.

109. Liu, K.J.; Qu, W.; Kadiiska, M.B. Role of oxidative stress in cadmium toxicity and

carcinogenesis. Toxicol. Appl. Pharmacol. 2009, 238, 209–214.

110. Toyokuni, S. Role of iron in carcinogenesis: Cancer as a ferrotoxic disease. Cancer Sci. 2008,

100, 9–16.

111. Dizdaroglu, M. Mechanisms of Free Radical Damage to DNA. In DNA and Free Radicals:

Techniques, Mechanisms and Applications; Aruoma, O.I., Halliwell, B., Eds.; OICA

International: Caribbean, St Lucia City, 1998; pp. 3–26.

112. Kawanishi, S.; Hiraku, Y.; Oikawa, S. Mechanism of guanine-specific DNA damage by

oxidative stress and its role in carcinogenesis and aging. Mutat. Res. Rev. Mutat. Res. 2001, 488,

65–76.

113. Delaney, S.; Jarem, D.A.; Volle, C.B.; Yennie, C.J. Chemical and biological consequences of

oxidatively damaged guanine in DNA. Free Radic. Res. 2012, 46, 420–441.

114. Jackson, J.H. Potential molecular mechanisms of oxidant-induced carcinogenesis. Environ.

Health Perspect. 1994, 102, 155–158.

115. Malins, D.; Polissar, N.L.; Gunselman, S.J. Progression of human breast cancers to the metastatic

state is linked to hydroxyl radical-induced DNA damage. Proc. Natl. Acad. Sci. USA 1996, 93,

2557–2563.

Int. J. Environ. Res. Public Health 2013, 10 3905

116. Willett, W.C.; Stampeer, M.J.; Colditz, E.A.; Rosner, C.H.; Hennekens, C.H.; Speizer, F.E.

Dietary fat and the risk of breast cancer. New Engl. J. Med. 1987, 316, 22–28.

117. Willett, W.C. The search for the causes of breast and colon cancer. Nature 1989, 338, 389–394.

118. Willett, W.C. Diet and cancer. Oncologist 2000, 5, 393–404.

119. Carracedo, A.; Cantley, L.C.; Pandolfi, P.P. Cancer metabolism: Fatty acid oxidation in the

limelight. Nat. Rev. Cancer 2013, 13, 227–232.

120. Ishii, H.; Fukumor, N.; Horie, S.; Suga, T. Effects of fat content in the diet on hepatic

peroxisomes of the rat. Biochim. Biophys. Acta 1980, 617, 1–11.

121. Esterbauer, H.; Ecki, P.; Ortner, A. Possible mutagens derived from lipid precursors. Mutat. Res.

1990, 238, 223–233.

122. Clayson, D.B.; Mehta, R.; Iverson, F. Oxidative DNA damage-the effect of certain genotoxic and

operationally non-genotoxic carcinogens. Mutat. Res. 1994, 317, 25–42.

123. Wang, M.Y.; Liehr, J.G. Lipid hydroperoxide-induced endogenous DNA adducts in hamsters:

Possible mechanim of lipid hydroperoxide-mediated carcinogenesis. Arch. Biochem. Biophys.

1995, 316, 38–46.

124. Bartsch, H.; Nair, J.; Owen, R.W. Exocyclic DNA adducts as oxidative stress markers in colon

carcinogenesis: Potential role of lipid peroxidation, dietary fat and antioxidants. Biol. Chem.

2002, 383, 915–921.

125. Marnett, L.J. Lipid peroxidation-DNA damage by malondialdehyde. Mutat. Res. 1999, 424,

83–95.

126. Shamberger, R.J.; Andreone, T.L.; Willis, C.E. Antioxidants and cancer: IV. Initiating activity of

malondialdehyde as a carcinogen. J. Natl. Cancer Inst. 1974, 53, 1771–1773.

127. Basu, A.K.; Marnett, L.J. Unequivocal demonstration that malondialdehyde is a mutagen.

Carcinogenesis 1983, 4, 331–333.

128. Marnett, L.J.; Hurd, M.C.; Hollstein, D.E.; Levin, H.; Esterbauer, H.; Ames, B.N. Naturally

occurring carbonyl compounds are mutagens in Salmonella tester strain TA104. Mutat. Res.

1985, 148, 25–34.

129. Nair, V.; Turner, G.A.; Offerman, R.J. Novel adducts from modification of nuclei acid bases by

malondialdehyde. J. Am. Chem. Soc. 1984, 106, 3370–3371.

130. Fink, S.P.; Reddy, G.R.; Marnett, L.J. Mutagenicity in Escherichia coli of the major DNA adduct

derived from the endogenous mutagen malondialdehyde. Proc. Natl. Acad. Sci. USA 1997, 94,

8652–8657.

131. Nair, U.; Bartsch, H.; Nair, J. Lipid peroxidation-induced DNA damage in cancer-prone

inflammation diseases: A review of published adduct types and levels in humans. Free Radic.

Biol. Med. 2007, 43, 1109–1120.

132. Blackburn, E.H. Structure and function of telomeres. Nature 1991, 350, 569–573.

133. Blackburn, E.H. Telomere states and cell fates. Nature 2000, 408, 53–56.

134. Blackburn, E.H. Switching and signaling at the telomere. Cell 2001, 106, 661–673.

135. Oikawa, S.; Kawanishi, S. Site-specific DNA damage at GGG sequence by oxidative stress may

accelerate telomere shortening. FEBS Lett. 1999, 453, 365–368.

136. Houben, J.M.J.; Moonen, H.J.J.; van Schooten, F.J.; Hageman, G.J. Telomere length assessment:

Biomarker of chronic oxidative stress? Free Radic. Biol. Med. 2008, 44, 235–246.

Int. J. Environ. Res. Public Health 2013, 10 3906

137. Von Zglinicki, T.; Martin-Ruiz, C.M.; Saretzki, G. Telomeres, cell senescence and human

ageing. Signal Transduct. 2005, 3, 103–114.

138. Von Zglinicki, T.; Martin-Ruiz, C.M. Telomeres as biomarkers for ageing and age-related

diseases. Curr. Mol. Med. 2005, 5, 197–203.

139. Smogorzewska, A.; de Lange, T. Different telomere damage signaling pathways in human and

mouse cells. EMBO J. 2002, 21, 4338–4348.

140. De Lange, T. Telomere-related genome instability in cancer. Cold Spring Harb. Symp. Quant.

Biol. 2005, 70,197–204.

141. Prescott, J.; Wentzensen, I.M.; Savage, S.A.; de Vivo, I. Epidemiologic evidence for a role of

telomere dysfunction in cancer etiology. Mutat. Res. 2012, 730, 75–84.

142. Cheng, A.L.; Deng, W. Telomere dysfunction, genome instability and cancer. Front. Biosci.

2008, 13, 2075–2090.

143. Blasco, M.A.; Hahn, W.C. Evolving views of telomerase and cancer. Trends Cell Biol. 2003, 13,

289–294.

144. Hou, L.; Wang, S.; Dou, C.; Zhang, X.; Yu, Y.; Zheng, Y.; Avula, U.; Hoxha, M.; Díaz, A.;

McCracken, J.; et al. Air pollution exposure and telomere length in highly exposed subjects in

Beijing, China: A repeated-measure study. Environ. Int. 2012, 48, 71–77.

145. Grahame, T.J.; Schlesinger, R.B. Oxidative stress-induced telomeric erosion as a mechanism

underlying airborne particulate matter-related cardiovascular disease. Part. Fibre Toxicol. 2012,

9, 21–28.

146. Grahame, T.J.; Schlesinger, R.B. Telomere susceptibility to cigarette smoke-induced oxidative

damage and chromosomal instability of mouse embryos in vitro. Free Radic. Biol. Med. 2010,

48, 1663–1676.

147. Berin, G.; Averbeck, D. Cadmium: Cellular effects, modifications of biomolecules, modulation

of DNA repair and genotoxic consequences (a review). Biochimie 2006, 88, 1549–1559.

148. Klaunig, J.E.; Kamendulis, L.M.; Hocevar, B.A. Oxidative stress and oxidative damage in

carcinogenesis. Toxicol. Pathol. 2010, 38, 96–109.

149. Holloway, J.W.; Savarimuthu, F.S.; Fong, K.M.; Yang, I.A. Genomics and the respiratory effects

of air pollution exposure. Respirology 2012, 17, 590–600.

150. Anisimov, V.N. The relationship between aging and carcinogenesis: A critical appraisal.

Crit. Rev. Oncol. Hematol. 2003, 45, 277–304.

151. Martien, S.; Abbadie, C. Acquisition of oxidative DNA damage during senescence: The first step

toward carcinogenesis. Ann. N. Y. Acad. Sci. 2007, 1119, 51–63.

152. Pacheco, K.A. Epigenetics mediate environment: Gene effects on occupational sensitization.

Curr. Opin. Allergy Clin. Immunol. 2012, 12, 111–118.

153. Darnell, J.E. Transcription factors targets for cancer therapy. Nat. Rev. Cancer 2002, 2, 740–749.

154. Kensler, T.W.; Wakabayashi, N.; Biswal, S. Cell survival responses to environmental stresses via

the keap1-Nrf2-ARE pathway. Ann. Rev. Pharmacol. Toxicol. 2007, 47, 89–116.

155. DeNicola, G.M.; Karreth, F.A.; Humpton, I.J.; Gopinathan, A.; Wei, C.; Frese, K.; Mangal, D.;

Yu, K.H.; Yeo, C.J.; Calhoun, E.S.; et al. Oncogene-induced Nrf2 transcription promotes ROS

detoxification and tumorigenesis. Nature 2011, 475, 106–109.

156. Lau, A.; Villeneuve, N.F.; Sun, Z.; Wong, P.K.; Zhang, D.D. Dual roles of Nef2 in cancer.

Pharmacol. Res. 2008, 58, 262–270.

Int. J. Environ. Res. Public Health 2013, 10 3907

157. Hsu, T.C.; Young, M.R.; Cmarik, J.; Colburn, N.H. Activator protein 1 (AP-1)- and nuclear

factor kappaB (NF-kappaB)-dependent transcriptional events in carcinogenesis. Free Radic. Biol.

Med. 2000, 28, 1338–1348.

158. Dhar, A.; Young, M.R.; Colburn, N.H. The role of AP-1, NF-kappaB and ROS/NOS in sking

carcinogenesis: The JB6 model is predictive. Mol. Cell Biochem. 2002, 234–235, 185–193.

159. Sethi, G.; Sung, B.; Aggrawal, B.B. Nuclear factor-kappaB activation: From bench to bedside.

Exp. Biol. Med. 2008, 238, 21–31.

160. Lee, C.H.; Jeon, Y.T.; Kim, S.H.; Song, Y.S. NF-kappaB as a potential molecular target for

cancer therapy. Biofactors 2007, 29, 19–35.

161. Wang, H.; Chu, C.H. Effect of NF-kappaB signaling on apoptosis in chronic

inflammation-associated carcinogenesis. Curr. Cancer Drug. Targets 2010, 10, 593–599.

162. Mabjeesh, N.J.; Amir, S. Hypoxia-inducible factor (HIF) in human carcinogenesis. Histol

Histopathol. 2007, 22, 559–572.

163. Kimbro, K.S.; Simons, J.W. Hypoxia-inducible factor-1 in human breast and prostate cancer.

Endocr. Relat. Cancer 2006, 13, 739–749.

164. Philip, B.; Ito, K.; Moreno-Sanchez, R.; Ralph, S.J. HIF expression and the role of hypoxic

microenvironments within primary tumours as protective sites driving cancer stem cell renewal

and metastatic progression. Carcinogenesis 2013, 34, 1699–1707.

165. Inoue, K.; Kurabayashi, A.; Shuin, T.; Ohtsuki, Y.; Furihata, M. Overexpression of p53 protein

in human tumors. Med. Mol. Morphol. 2012, 45, 115–123.

166. Maillet, A.; Perraiz, S. Redox regulation of p53, redox effectors regulated by p53: A subtle

balance. Antiox. Redox Signal. 2012, 16, 1285–1294.

167. Lanni, C.; Racchi, M.; Memo, M.; Gavoni, S.; Uberti, D. p53 at the crossroads between cancer

and neurodegeneration. Free Radic. Biol. Med. 2012, 52, 1727–1733.

168. Suzuki, S.; Tanaka, T.; Poyurovsku, M.V.; Nagano, H.; Mayama, T.; Ohkubo, S. Phosphate-

activated glutaminase (GLS2), ap53-inducible regulator of glutamine metabolism and reactive

oxygen species. Proc. Natl. Acad. Sci. USA 2010, 107, 7461–7466.

© 2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article

distributed under the terms and conditions of the Creative Commons Attribution license

(http://creativecommons.org/licenses/by/3.0/).